Next day remove marinating chicken and allow to come to room temperature. Add oil to a large pan and heat on medium high heat. When sizzling, add chicken to pan and brown. Cook to just done. Remove chicken to a bowl.

Add ghee and onions to the pan and soften on medium heat.

Add garlic and ginger to pan. Stir for 30 seconds until fragrant. Add Garam masala, cumin and red chili powder to pan. Stir for 30 seconds until fragrant.

Add diced tomatoes to pan and simmer for 10 minutes while occasionally stirring. If mixture gets too dry add in some chicken stock.

Transfer pan contents to a blender. Separate cashews from the water and add to the blender. Put blender on high until sauce is smooth. Return sauce to the pan. It will be thick.